As a conventional vehicle peripheral monitoring device, there is a known device in which, when an illumination detection means detects illuminance above a predetermined level, a display device displays the state of a monitored area imaged by an imaging means, and when the illuminance is below the predetermined level, the display device displays obstacle information acquired by illumination with pattern light, imaging of the reflected light, and data processing (see, for example, patent reference 1).
A system that performs optical distance measurement by use of speckle patterns is also known. This system projects a primary speckle pattern from an illumination assembly into a target area, captures a plurality of reference images of the primary speckle pattern at different distances in the target area from the illumination assembly, captures a test image of the primary speckle pattern projected onto the surface of an object in the target area, compares the test image with the reference images to identify the reference image in which the primary speckle pattern most closely matches the primary speckle pattern in the test image, and estimates the position of the object on the basis of the distance of the identified reference image from the illumination assembly (for example, patent reference 2).